Optical waveguide devices are indispensable in various high technology industrial applications, and especially in telecommunications. In recent years, these devices, including planar waveguides, and two or three dimensional photonic crystals are being used increasingly in conjunction with conventional optical fibers. In particular, optical waveguide devices based on high refractive index contrast or high numerical aperture (NA) waveguides are advantageous and desirable in applications in which conventional optical fibers are also utilized. However, there are significant challenges in interfacing optical high NA waveguide devices, including chiral optical fiber devices, with conventional low index contrast optical fibers. Typically, at least two major obstacles must be dealt with: (1) the difference between the sizes of the optical waveguide device and the conventional fiber (especially with respect to the differences in core sizes), and (2) the difference between the NAs of the optical waveguide device and the conventional fiber. Failure to properly address these obstacles results in increased insertion losses and a decreased coupling coefficient at each interface.
For example, conventional optical fiber based optical couplers, such as shown in FIG. 6 (Prior Art) are typically configured by inserting standard optical fibers (used as input fibers) into a capillary tube comprised of a material with a refractive index lower than the cladding of the input fibers. There are a number of significant disadvantages to this approach. For example, a fiber cladding-capillary tube interface becomes a light guiding interface of a lower quality than interfaces inside standard optical fibers and, therefore, can be expected to introduce optical loss. Furthermore, the capillary tube must be fabricated using a costly fluorine-doped material, greatly increasing the expense of the coupler.
A commonly assigned U.S. Pat. No. 7,308,173, entitled “OPTICAL FIBER COUPLER WITH LOW LOSS AND HIGH COUPLING COEFFICIENT AND METHOD OF FABRICATION THEREOF”, which is hereby incorporated herein in its entirety, advantageously addressed all of the above issues by providing various embodiments of a novel optical fiber coupler capable of providing a low-loss, high-coupling coefficient interface between conventional optical fibers and optical waveguide devices.
Nevertheless, a number of challenges still remained. With the proliferation of optical devices with multiple waveguide interfaces (e.g., waveguide arrays), establishing low-loss high-accuracy connections to arrays of low or high NA waveguides often provide problematic, especially because the spacing between the waveguides is very small making coupling thereto all the more difficult. The commonly assigned U.S. Pat. No. 8,326,099, entitled “OPTICAL FIBER COUPLER ARRAY”, issued Dec. 4, 2012, which is hereby incorporated herein by reference in its entirety, addressed the above challenge by providing, in at least a portion of the embodiments thereof, an optical fiber coupler array that provides a high-coupling coefficient interface with high accuracy and easy alignment between an optical waveguide device having a plurality of closely spaced high NA waveguide interfaces, and a plurality of optical fibers each having low numerical apertures separated by at least a fiber diameter. While the '099 Patent already teaches the coupler, which is capable to independently control waveguide NAs and channel-to-channel spacing, it did not specifically address the full extent of configurability with respect to interfacing with plurality of optical fibers, possible use of its disclosed novel structures and inventive methodologies for fabrication thereof.
In addition, it is important to note that security of fiber optic links has attracted growing attention in recent years. However, the commonly utilized conventional methods of increasing security against unauthorized fiber optic link tapping (e.g., signal encryption, intrusion monitoring, and fiber link protection through physical security) have a number of disadvantages that heretofore remain unaddressed.
While the '865 Application effectively addresses various techniques for optimizing the inventive coupler array comprising vanishing cores (for example to produce novel pitch reducing optical fiber array (“PROFA”) interconnects), it should be noted that various embodiments of the inventive coupler array disclosed therein could be further advantageously configured and/or modified to provide secure optical fiber link components.
Accordingly, it would be advantageous to provide various embodiments of an inventive PROFA-based optical fiber link component that is “physically untappable”.